Question: What does a huge cloud of around 10 billion stars forming one of the most important, massive parts of the galaxy look like? Answer: a peanut.
Two groups of astronomers have used European Southern Observatory (ESO) data to create the best three-dimensional map of the center the Milky Way yet. Their research suggests that the inner regions of our galaxy take on a peanut-like, or X-shaped appearance from some angles.
The galactic bulge is difficult for astronomers to view because — from our vantage point within the galactic disc, and at a distance of around 27,000 light years — it is heavily obscured by dense clouds of dust and gas. By observing longer wavelength light such as infrared radiation, though, astronomers are able to obtain a good picture of the center of the galaxy despite these interferences.
The two independent teams arrived at the same conclusion but using different techniques and data sets.
The first team, from the Max Planck Institute of Extraterrestrial Physics (MPE) in Germany, used data from the ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) located at the Paranal Observatory in Northern Chile. The survey — which is publicly available to the scientific community — took advantage of much greater star visibility than previous research and the team from MPE used this to make a three-dimensional map of the bulge.
The second group, led by Universidad Católica PhD student Sergio Vásquez, took a different approach but reached the same conclusion regarding the massive star cloud’s shape. The Chilean-led team compared images taken eleven years apart allowing it to measure tiny shifts caused by the motions of the bulge stars across the sky. When combined with measurements of the movements of the same stars towards or away from the Earth the team was able to map out the motions of more than 400 stars in three dimensions.
“This is the first time that a large number of velocities in three dimensions for individual stars from both sides of the bulge have been obtained,” concludes Vásquez. “The stars we have observed seem to be streaming along the arms of the X-shaped bulge as their orbits take them up and down and out of the plane of the Milky Way. It all fits very well with predictions from state-of-the-art models.”
Astronomers theorize that our galaxy was originally a pure disc of stars which formed a long narrow feature, known as a bar, across its center billions of years ago. The inner part of this bar then buckled up to form the three dimensional peanut shape revealed by recent studies.
Due to its almost non-existent humidity and clear skies, the Atacama is the world’s premier location for astronomy. Chile is home to almost half the world’s telescope infrastructure, and this is set to increase to over two thirds in the next decade.